Acoustical ceiling tiles can be made by a wet pulp molding or cast process such as described in U.S. Pat. No. 1,769,519. In accordance with this process, a molding composition comprising granulated mineral wool fibers, fillers, colorants and a binder (e.g. starch gel), is prepared for molding or casting the tile. The composition is placed upon suitable trays which have been covered with paper or a metallic foil and then the composition is screeded to a desired thickness with a screed bar or roller. A decorative surface, such as elongated fissures, may be provided by the screed bar or roller. The trays filled with the mineral wool composition are then placed in an oven to dry or cure.
U.S. Pat. No. 4,585,685 discloses acoustical ceiling tiles which are produced by applying aggregate material to the surface of a dry-formed web comprising a fibrous material and an organic binder, and consolidating the composite material such that the aggregate material is embedded in the web. In Example 1 of this patent, a wetlaid board was prepared by means known in the art using a fourdrinier machine. While the dewatered sheet resided on the wire, a dry layer of perlite was applied, the layered sheet was passed through a press section, and the consolidated sheet was separated from the wire. The sheet was then dried in a conventional manner by passing it through a heating tunnel. The sheet was subjected to an acoustics test (ASTM C423) and its NRC (noise reduction coefficient) was 0.28. The patentees concluded that this acoustical performance was unacceptable.
It is an object of this invention to provide a cast acoustical tile having an abuse-resistant surface formed from aggregate particles and having an excellent sound absorption value.
It is another object of this invention to provide a process for making an abuse-resistant ceiling tile wherein aggregate particles are applied to a wet ceiling tile substrate after which they are pressed with a roll and/or smooth plates to bond the aggregate particles to the substrate.
It is a further object of this invention to provide an abuse-resistant, cast ceiling tile having a sound absorption value (NRC) of at least about 0.50.
These and other objects will be apparent to persons skilled in the art in view of the description that follows.